FIG. 1 shows a circuit 1C of the related art having a high frequency transmission line 103 with an open-ended stub 104P formed on an insulation layer 102. The open-ended stub 104P is branched from the transmission line 103 through which high-frequency signals are transmitted from an input end E1 to an output end E2. FIG. 1 also shows a pad 105 that is formed at the end of the open-ended stub 104P for signal analysis purposes. A signal analysis circuit (not shown) is connected to the pad 105 so that the signal in the transmission line 103 can be acquired through the pad 105 and analyzed using the signal analysis circuit.
Part of the signals transmitted through the open-ended stub 104P is, however, reflected by the end E3 of the open-ended stub 104P. The reflected signal is not desirable because it interferes with and deteriorates the main signal flowing in the transmission line 103 from the input end E1 to the output end E2. Thus, in the related art, in order to reduce the adverse effect of the reflected signal, the length L of the open-ended stub 104P is shortened so as to increase the frequency of the reflected signal because interference from the reflected signal can be acceptable if it is at a high enough frequency. However, because the open-ended stub is provided for analysis purposes as described above, there is a limit on how short the length L of the open-ended stub.